1. Technical Field
The present disclosure relates to communication devices, and more particularly to selection/reselection of a cell for attempting to connect in a congested cellular environment.
2. Description of the Related Art
Wireless communications systems are widely deployed to provide various types of communication such as voice, packet data, and so on. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), or other multiple access techniques. Such systems can conform to standards such as Third-Generation Partnership Project 2 (3GPP2, or “cdma2000”), Third-Generation Partnership (3GPP, or “W-CDMA”), or Long Term Evolution (LTE). In the design of such communications systems, it is desirable to maximize the capacity, or the number of users the system can reliably support, given the available resources.
In a cellular communication system, a geographical region is divided into a number of cells served by base stations. The base stations are interconnected by a fixed network which can communicate data between the base stations as well as a core network. A mobile station or user equipment is served via a radio communication link from the base station or node of the cell within which the mobile station is camped on. Communication from a mobile station to a base station is known as the uplink, and communication from a base station to a mobile station is known as the downlink.
The Random Access Channel (RACH) is a contention-based channel for initial uplink transmission, i.e., from User Equipment (UE) to a base station. The RACH can be used for several purposes, such as to access the network, to request resources, to carry control information, to adjust the time offset of the uplink, to adjust the transmitted power, and to transmit small amounts of data; however, contention resolution is the key feature of the random access channel.
Many UEs can attempt to access a same base station simultaneously, leading to collisions. In some instances, too many users attempt to establish a connection to a same cell or base station using a RACH procedure or too few network interfaces for the cell or base station are available because too many users are already connected to the network. In these instances, the RACH procedures of the UE can fail repeatedly.